The PSI rating for the tire itself isn't the full story either. Your rim's will have PSI rating as well. Generally speaking, you don't run your tires at the max PSI rating.

Since you asked this in the cyclocross forum, I'm guessing your asking what PSI your cyclocross tires should be? I run 40 -55 PSI depending on the race course and weather. These are for 32 - 35 mm clinchers (Ritchey Crossmax's and Maxxix MiMo's.)

As for road, I run 23 mm clinchers at 115 - 120 PSI for racing (Mich Pro2Race) and 100 PSI on 25 mm clinchers at 100 PSI for training (Conti Gatorskins.)